If you have already sold the items it is too late to talk about the ebay satchels, as your items will need to be posted promptly and even if you order now, you won't get the satchels until about Friday.

So for anything ready to send now, you could use your own packaging and the ebay postage labels, that way you can pack, pay and have them ready to drop off at the PO tomorrow.   Just work out the calculated postage first, in case it is too expensive to send that way.

Otherwise you could buy the 3kg satchels at the PO but it is more expensive.   You could let us know the weight so could give more information.

In the meantime, order some ebay satchels so you will be ready next time.   They are quite cheap I think $4.20 will get you 20 ebay satchels, which you can use with the ebay labels, saving you some $$$.    However this won't be any good if your items don't fit!!